Greenland Ice Sheet Melt Characteristics Derived from Passive Microwave Data, Version 1

The Greenland ice sheet melt extent data, acquired as part of the NASA Program for Arctic Regional Climate Assessment (PARCA), is a daily (or every other day, prior to August 1987) estimate of the spatial extent of wet snow on the Greenland ice sheet since 1979. It is derived from passive microwave satellite brightness temperature characteristics using the Cross-Polarized Gradient Ratio (XPGR) of Abdalati and Steffen (1997). It is physically based on the changes in microwave emission characteristics observable in data from the Scanning Multi-channel Microwave Radiometer (SMMR) and the Special Sensor Microwave/Imager (SSM/I) instruments when surface snow melts. It is not a direct measure of the snow wetness but rather is a binary indicator of the state of melt of each SMMR and SSM/I pixel on the ice sheet for each day of observation. It is, however, a useful proxy for the amount of melt that occurs on the Greenland ice sheet. The data are provided in a variety of formats including raw data in ASCII format, gridded daily data in binary format, and annual and complete time series climatologies in gridded binary and GeoTIFF format. All data are in a 60 x 109 pixel subset of the standard Northern Hemisphere polar stereographic grid with a 25 km resolution and are available via FTP.格陵兰冰盖融雪范围数据集，为美国国家航空航天局（National Aeronautics and Space Administration, NASA）北极区域气候评估计划（Program for Arctic Regional Climate Assessment, PARCA）的产出数据之一，自1979年起以每日（1987年8月前为每隔一日）的频率，对格陵兰冰盖表面湿雪的空间分布范围进行估算。该数据集基于Abdalati与Steffen于1997年提出的交叉极化梯度比（Cross-Polarized Gradient Ratio, XPGR），由被动微波卫星亮温特征反演得到。其物理原理源自扫描多通道微波辐射计（Scanning Multi-channel Microwave Radiometer, SMMR）与专用传感器微波成像仪（Special Sensor Microwave/Imager, SSM/I）的观测数据：当地表积雪发生融化时，仪器可观测到微波辐射特征的变化。该数据集并非直接测量积雪湿度，而是为每日观测中冰盖上的每个SMMR与SSM/I像元的融化状态提供二元分类指示。但其仍可作为格陵兰冰盖实际融雪规模的有效替代指标。数据集提供多种格式版本，包含ASCII格式原始数据、二进制格式网格化每日数据，以及网格化二进制与GeoTIFF格式的年度及全时间序列气候学数据集。所有数据均采用分辨率为25km的标准北半球极方位立体投影网格的60×109像元子集形式，并可通过文件传输协议（File Transfer Protocol, FTP）获取。